The invention relates to electron beam apparatus. More particularly, the invention relates to a protective shield for use within or without the evacuated target chamber of an electron beam apparatus which is traversed by an electron beam having a high energy density.
The electron beam generated by electron guns operating with a high accelerating potential and at elevated beam intensity, is normally a relatively narrow beam with high energy density, even without electronic focusing. The beam remains narrow and the energy density remains high along the entire path traversed by the beam from the gun to the target chamber. As a consequence, the beam is capable of causing damage or destruction of parts of the apparatus, for example a holding mechanism or the target chamber wall, if it is inadvertently permitted to strike these objects, due to operating errors for example. Damage may still occur even if the impact occurs at a substantially greater distance than the intended target surface.
It is known in the art to provide protection against beam damage by installing relatively thick metal plates as beam catchers. These plates require a relatively large space and thus limit the motion of the workpiece within the target chamber as well as being subject to several other disadvantages.